Orientation dependence of yield stress in 4.4% silicon iron single crystals

Abstract

Single crystals of a 4.4%Si-Fe with systematically selected orientations were deformed in tension or compression at room temperature. Slip bands were observed to be nearly parallel to traces of either {110} or {112} plane in most specimens. Two anomalous results were obtained on orientation dependence of yield stress. First, the Schmid law did not hold for the {110}〈111〉 slip system, that is, the critical resolved shear stress increased as the plane of maximum Schmid factor deviated from the {110} plane towards the neighbouring {112} cross slip plane. This is discussed in relation to differences in the dragging stress for the motion of screw dislocations due to differences in the density of jogs which were produced by cross slip. The difference in density of dragging points among specimens with different stress axes was, in fact, observed by electron microscopy using thin foils parallel to slip planes. Secondly, the critical resolved shear stress for a {112}〈111〉 slip in the twinning shear direction was about 13% lower than that in the opposite direction. This fact is tentatively attributed to different Peierls -Nabarro stress between the two opposite senses of motion of a dislocation on a {112} plane.